Nanotube assembly

ABSTRACT

Methods and articles providing for precise aligning, positioning, shaping, and linking of nanotubes and carbon nanotubes. An article comprising: a solid surface comprising at least two different surface regions including: a first surface region which comprises an outer boundary and which is adapted for carbon nanotube adsorption, and a second surface region which is adapted for preventing carbon nanotube adsorption, the second region forming an interface with the outer boundary of the first region, at least one carbon nanotube which is at least partially selectively adsorbed at the interface. The shape and size of the patterns on the surface and the length of the carbon nanotube can be controlled to provide for selective interfacial adsorption.

RELATED APPLICATIONS

This application claims priority to provisional application Ser. No.60/741,837 to Mirkin et al. filed Dec. 2, 2005, which is incorporatedherein by reference.

STATEMENT OF FEDERAL FUNDING

This invention was made with government support under Grant No.EEC-0118025 awarded by the National Science Foundation; Grant Nos.F49620-00-1-0283 and F49620-01-1-0401 awarded by the Air Force Office ofScientific Research; and Grant No. 1 DP1OD00285-01 awarded by theNational Institutes of Health. The government has certain rights in theinvention.

BACKGROUND

Single-walled carbon nanotubes (SWNTs) are of commercial interest inapplications ranging from ultra-small electronic and sensing devices tomultifunctional materials (1). Examples include field effect transistors(2), field emission displays (7), and chemical sensors (3,6).Integration of the nanotube material depends on the ability to controlthe placement, orientation, and shape of the nanotube components withinthe context of the device on the micrometer- to nanometer-length scale.Positional control over large areas is important. Depending on theintended application, one wants to pattern SWNTs as individual tubes(3,4), small bundles (5), or thin films (6, 8, 9). SWNTs are but oneexample of nanotechnology building blocks, and other examples includenanotubes generally and nanowires.

Previous work has shown that individual carbon nanotubes can bepositioned (10), bent (11), and even welded (12) with nanometer accuracyby using scanning probe instruments. This level of manipulation can belimited to serial and therefore slow processes than span relativelyshort distances (100 microns). Other assembly methods such asLangmuir-Blodgett techniques (13), external field assisted routes(14-19), electrospinning (20), transfer printing (21), and DNA templates(22, 23) also have been used for nanotube assembly. These parallelmethods address the speed limitation posed by conventional scanningprobe techniques, but thus far are quite limited with respect toregistration control and have demonstrated only coarse placementcapabilities.

One approach is to use patterned chemical templates to assemble SWNTsfrom solutions. For example, SWNTs can be positioned along straight linefeatures comprised of amine-terminated self-assembled monolayers (SAMs)(9, 24-27). See also US patent publication 2004/0166233 (“DepositingNanowires on a Substrate”) to Hong.

Additional background patent literature includes US Patent publications2004/0245209 to Jung et al (published Dec. 9, 2004); 2005/0269285 toJung et al. (published Dec. 8, 2005); and 2004/0101469 to Demers(published May 27, 2004).

A need exists, however, to better simultaneously control the position,shape, and/or linkage of nanotubes, nanowires, and in particular carbonnanotubes including SWNTs on the sub-micron scale to better providesophisticated architectures including for example rings, electronicinterconnects, and structured thin films.

A need exists to better adapt nanolithography to carbon nanotubeincluding SWNT placement technology (28,29).

A listing of references is provided later herein for literaturecitations.

SUMMARY

A variety of embodiments are provided including, among other things,articles, methods of making articles, methods of using articles, andcompositions.

One embodiment provides an article comprising: a solid surfacecomprising at least two different surface regions including: a firstsurface region which comprises an outer boundary and which is adaptedfor carbon nanotube adsorption, and a second surface region which isadapted for preventing carbon nanotube adsorption, the second regionforming an interface with the outer boundary of the first region, atleast one carbon nanotube which is at least partially selectivelyadsorbed at the interface. The first region can comprise hydrophilicgroups which can be carboxylic groups. The second region can comprisehydrophobic groups which can be alkyl groups.

Another embodiment provides an article comprising: a solid surfacecomprising at least two different surface regions including: a firstsurface region which comprises an outer boundary and which is adaptedfor carbon nanotube adsorption, and a second surface region which isadapted for preventing carbon nanotube adsorption, the second regionforming an interface with the outer boundary of the first region, atleast one carbon nanotube which is sufficiently long with respect to thesize and shape of the first surface region so that it is at leastpartially selectively adsorbed at the interface.

Another embodiment provides a method comprising: providing a solidsurface comprising at least two different surface regions including: afirst surface region which comprises an outer boundary and which isadapted for carbon nanotube adsorption, and a second surface regionwhich is adapted for preventing carbon nanotube adsorption, the secondregion forming an interface with the outer boundary of the first region,providing a liquid composition comprising a plurality of carbonnanotubes in at least one liquid solvent, placing the liquid compositionon the solid surface, so that at least one carbon nanotube adsorbs tothe surface, removing the at least one liquid solvent, wherein the atleast one carbon nanotube is at least partially selectively adsorbed atthe interface.

Provided herein are methods of using the interface of two-componentmolecular templates for assembly and manipulation of nanotubes andnanowires, including positioning, orientation, shaping, and linking.

Advantages include among other things ability to align, position, orientshape, and link nanotubes and nanowires. In particular, carbon nanotubescan be linked together based on strong van der Waals interactionsbetween the nanotubes to form ropes. Single conductive pathways can beformed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the directed assembly process. (a)Schematic illustrating the rolling of a drop of theSWNTs/1-2-dichlorobenzene solution on a two-component surface comprisingCOOH-SAM and CH3-SAM (b) the SWNTs are selectively transported to theCOOH-SAM and pinned at its boundary with the ODT SAM. Upon drying, theSWNT bends to precisely follow the molecular path of the patternedCOOH-SAM.

FIG. 2 shows SWNTs assembled into rings and nano letters. (left) AFMtapping mode topographic images, (upper) and height profiles (lower) ofSWNT rings in a 5×5 array. (right) A zoom-in view of one SWNT ring(lower) and a molecular model of a coiled SWNT. (upper)

FIG. 3 shows the assembly of SWNTs depends on the surface functionalgroups. (a-c) AFM tapping mode topographic images of a series ofsubstrates with one micron MHA dot arrays passivated with MUO (a), ODT(b), and PEG-SH (c). These dots show that ODT is the superiorpassivation layer. (d-f) AFM phase images of a second series of twomicron dots of MUO (d), AUT (e), and PEG-SH (f), passivated with ODT.None of these show the better SWNT assembly observed fro the MHA/ODTsystem in b. (insets) Shown are zoom-in images of a selected dot. Allimages were taken at a scan rate of 0.5 Hz. The height scale is 20 nm,and the phase lag is 10°.

FIG. 4 shows AFM tapping mode topographic images of selected SWNTarrays. (a) Parallel aligned SWNTs with a line density approaching5.0×10⁷/cm². (b) Linked SWNTs following MHA lines (20 microns×200 nm)spaced by two microns, one micron, and 600 nm. (c) random linestructure, showing the precise positioning, bending, and linking ofSWNTs to a MHA affinity template. All images were taken at a scan rateof 0.5 Hz. The height scale is 20 nm.

FIG. 5 shows SWNT filtration membranes. (a) AFM topographic image of aSWNT membrane with 600±50-nm diameter pores spanning an area of 10×10microns. (b) corresponding Raman image showing SWNT spectroscopicsignatures. The false color topography represents the integrated Ramanintensity over 1.320-1,620 cm−1. (c and d) Representative AFMtopographic images of a SWNT network with 1.6±0.1 micron-diameter poresspanning an area of 1×2 cm. All AFM images were recorded at a scan rateof 0.5 Hz, and the height scales are 20 nm.

FIG. 6 shows AFM tapping mode phase and topographic images of SWNTnanoarcs. Phase image of a 2×2 MHA ring array, illustrating that shortSWNTs bend to form sub-micron sized arcs without closing the rings.(inset) An enlarged topographic image of one of these rings. All imageswere taken at a scan rate of 0.5 Hz. The height scale is 20 nm, and thephase lag is 25°.

FIG. 7 shows AFM tapping mode topographic images of SWNT letters. (a)whole array (45×45 microns), including the letters S, Z, U, C, N, and L.(b-i) Zoom in view of individual letters. Note that b and d are thepatterned MHA nanoletters before SWNT deposition. All images were takenat a scan rate of 0.5 Hz. The height scale is 20 nm.

FIG. 8 shows AFM tapping mode topographic images illustrating the dotsize influence for trapping SWNTs. (a) array of 3×3 dots with sizes of 1micron, 875 nm, 650 nm, 500 nm, 375 nm, 250 nm, 200 nm, 140 nm, and 90nm. (b-j) zoom-in views of each individual dot. The height scale is 20nm. All images were taken at a scan rate of 0.5 Hz.

FIG. 9 shows AFM tapping mode topographic images illustrating the linesize influence for trapping SWNTs. (a) array of 3×2 lines with sizes ofthree microns×750 nm, 2.2 microns×400 nm, 1.5 microns×250 nm, 875 nm×150nm, 450 nm×120 nm, and 450 nm×100 nm. (b-g) zoom-in views of eachindividual line. All images were taken at a scan rate of 0.5 Hz. Theheight scale is 20 nm.

FIG. 10 shows affinity of SWNTs to different alkanethiol SAMs formed ongold substrates. (a) MHA. (b) ODT. (c) PEG-SH. (d) AUT. All images weretaken at a scan rate of 0.5 Hz. The height scale is 20 nm.

FIG. 11. SWNTs assembled along MHA line features that were defined byparallel DPN printing with a 26-pen array.

FIG. 12. AFM tapping mode topographic (a) and phase (b) images of a SWNTrandom circuit. This image is a zoom-in view of the array shown in FIG.4 c. The SWNTs precisely position, bend and link to follow the randompath of the MHA line. All images were taken at a scan rate of 0.5 Hz.The height scale in a is 20 nm and 20° of phase lag in b.

FIG. 13 illustrates a device for applying the carbon nanotubes withsolvent.

DETAILED DESCRIPTION Introduction

The contents of provisional patent application Ser. No. 60/741,837 filedDec. 2, 2005 to Mirkin et al., and the contents of Wang et al., PNAS,vol. 103, no. 7, 2026-2031, including supplementary materials, arehereby incorporated by reference in their entirety including figures andworking examples.

References cited herein are hereby incorporated by reference and can beused as appropriate by one skilled in the art in the practice of thepresent invention.

Nanostructured materials are described in The Chemistry ofNanostructured Materials, ed. Peidong Yang, including Chapter 4, CVDSythesis of Single Walled Carbon Nanotubes, page 101-126, and itsdescription of SWNTs, as well as references cited therein.

Microfabrication and nanofabrication is generally described in forexample Madou, Fundamentals of Microfabrication, The Science ofMiniaturization, 2^(nd) Ed., CRC, 2002.

Deposition methods, functionalizing surfaces, and nanowires aredescribed in for example Hong, Seunghun, US Patent Publication2004/0166233, Depositing Nanowires on a Substrate, which is herebyincorporated by reference in its entirety.

Solid Surface

The surface is not particularly limited as long as it can provide thefirst and second regions, and the interface between the first and secondregions, and carbon nanotube adsorption. Generally flat surfaces can beused. The surface can be generally flat in one area but then also havedepressions or protrusions in other areas. The surface can be generallysmooth and substantially free of rough areas. The surface can be a solidsurface; the surface can be the surface of a substrate. The surface canbe formed from a substrate which is either monolithic or comprisemultiple materials such as a series of layered materials, or it may besurface modified. The substrates can be metal or ceramic or inorganicsubstrates. Substrates can be adapted to have surface coatings includingself-assembled monolayers including those that provide organic tailgroups, unreactive tail groups, or reactive functional tail groups.Surface coatings can be organic materials, including low molecularweight and high molecular weight coatings. In particular, a solidsubstrate surface can be modified with self-assembled monolayers. Aninorganic or metallic substrate can be modified with an organic surfacelayer. Surfaces and substrates used in DPN printing can be used asdescribed in for example U.S. Pat. No. 6,827,979 to Mirkin et al., whichis hereby incorporated by reference.

The surface can be adapted for use in a final application such as forexample an electronics or transistor application. Hence, the surface cancomprise for example electrically conducting, electrically insulating,or semiconductor regions and elements including electrodes for use infield-effect transistors.

The first and second regions can be adapted to have different affinitiesfor adsorbing carbon nanotubes. For example, FIGS. 1 a and 1 b showsexamples of first and second regions. FIG. 1 a shows a side view of thesubstrate. FIG. 1 b shows a top view. The other figures show top views.

First Surface Region

The first surface region can comprise an outer boundary. The firstsurface region can be adapted for carbon nanotube adsorption. The typeof adsorption is not particularly limited and may be affected by whetherthe nanotube is surface functionalized. Physical adsorption or chemicaladsorption can be used. Adsorption based on Van Der Waals interactionscan be used.

The first region can be hydrophilic in nature by comprising hydrophilicfunctional groups at the substrate surface. The first region cancomprise polar functional groups. The groups can be for example selectedto provide for solvent wetting and low water contact angles (e.g., lessthan 90°). In particular, the first region can comprise carboxylfunctional groups, including in different forms including the anion oracid form or a neutral or basic form. Another example is aminofunctional groups. Mixtures of functional groups can be used.

The first region can be formed with use of patterning of self assembledmonolayer compounds including sulfur-on-gold type of patterning.Examples can be found in U.S. Pat. No. 6,827,979 to Mirkin et al. Thefunctional groups can be provided by compounds represented by X—S—Ywhere in X is adapted to bind to a substrate (e.g., sulfur binding togold), S is a spacer such as a —(CH₂)_(x)— spacer wherein x is 2-25, andY is a polar functional group like carboxyl.

Second Surface Region

The second region can be hydrophobic in nature by comprising hydrophobicgroups, or hydrophobic functional groups, at the substrate surface. Thesecond region can comprise non-polar functional groups. The surface canprovide for non-solvent wetting and high contact angles with water(e.g., over 90°) In particular, the second region can comprise alkylfunctional groups at the substrate surface. Another example isfluorinated compounds including perfluorinated and partiallyfluorinated. Mixtures can be used.

The second region can be formed with use of deposition or patterning ofself assembled monolayer compounds including sulfur-on-gold type ofpatterning. Examples can be found in U.S. Pat. No. 6,827,979 to Mirkinet al. The functional groups can be provided by compounds represented byX—S—Y where in X is adapted to bind to a substrate (e.g., sulfur bindingto gold), S is a spacer such as a —(CH₂)_(x)— spacer wherein x is 2-25,and Y is a non-polar functional group like methyl.

Carbon nanotubes generally will adsorb to the second surface far lessthan the first surface. The second surface helps prevent carbon nanotubeadsorption. In general, non-specific binding of CNTs should be avoided.

The second region forms an interface with the outer boundary of thefirst surface.

Particularly unexpected good results can be found with thecarboxylic/amino system for first and second regions, respectively.

Shapes for the Surface Regions

The first and second regions can be formed so that a variety of shapesand patterns are formed, including shapes and patterns for theinterface. The shapes can be either full shapes or can be hollowed outshapes. For example, a full dot can be formed as a first region, or thedot can be hollowed out so that the first region is a ring. The shapedcan be symmetric shapes like circles or lines, or non-symmetric shapes.The first region can be formed so that it has a perimeter which isenclosed. Periodic shapes and patterns can be made. The first surfaceregion can comprise a dot, a ring, a line, or a curvilinear structure.

The article can comprise a plurality of first surface regions, aplurality of second surface regions, and a plurality of interfaces. Forexample, a periodic array can be built. Combinatorial arrays can bebuilt. For example, a region can form a feature such as a dot or a line,and the article can comprise at least 2, at least 10, at least 100, orat least 1,000 features.

Interface Between First and Second Regions

The first and second regions are disposed next to each other so that aninterface is present between the first and second region. In particular,the first surface region comprises an outer boundary, and the secondregion forms an interface with the outer boundary of the first region.In general, the interface is distinct and clean, although in practicedepending on the analytical method used to examine the interface theinterface may not be perfect and an interfacial region can bedetermined.

An exemplary interface is created by two self-assembled monolayersdisposed next to each other. The first and second regions can begenerally co-planar so that the interfacial region is smooth and doesnot have a drop-off or ridge.

FIGS. 1 a and 1 b show examples of the interfacial region.

Carbon Nanotube

Carbon nanotubes are known in the art including for example, (1) Ajayan,P. M., Nanotubes from Carbon, Chemical Review, 1999, 99(7), p.1787-1800, and (2) Dai, H. J., Carbon Nanotubes, Opportunities andChallenges, Surface Science, 2002, 500 (1-3), p. 218-241, and (3)Baughman et al, Science, 297, 787. In addition, carbon nanotubes aredescribed in Marc J. Madou's Fundamentals of Microfabrication, TheScience of Miniaturization, 2nd Ed., pages 454-455, including carbonnanotube preparation by CVD from patterned catalysts. This Madou textalso describes microlithography and nanolithography, and the use ofcarbon nanotubes at tips of AFM and STM probes. Carbon nanotubes arealso described in the text, Carbon Nanotubes, by Dresselhaus et al.,Springer-Verlag, 2000. See also, Special-Section, “Carbon Nanotubes”Physics World, vol. 13, pp. 29-53, 2000. Carbon nanotubes can besingle-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes(MWNTs), nanohorns, nanofibers, or nanotubes. They can be conducting orsemiconducting depending on the form of the nanotube. They can be open,closed, and have different kinds of spiral structure. They can be inzigzag and armchair form and have varying steepness which alters thechiral form. Additional description is provided in US Patent Publication20060115640 to Yodh et al.

Carbon nanotubes can be obtained commercially. The HiPco process can beused to prepare carbon nanotubes (see for example Rice University andCarbon Nanotechnology, Inc.). In this procedure, high pressure and hightemperature CO with Fe(CO)5 as a catalyst precursor produce high-qualitySWNTs.

Carbon nanotubes can be used both as individual carbon nanotubes andalso as a plurality of carbon nanotubes, wherein a statistical averageand deviation from the mean can be used to characterize the nanotubes.

In particular, the carbon nanotube can be a single wall carbon nanotube.

The carbon nanotube can be derivatized before use.

The carbon nanotube can be purified before use.

The length of the carbon nanotube is not particularly limited but can befor example, about 10 nm to about 5 microns, or about 25 nm to about 5microns, or about 10 nm to about 200 nm, or about 25 nm to about 200 nm.

The carbon nanotube, or the plurality of nanotubes, can form structureswhich have a height of about 10 nm or less, or about 5 nm or less, orabout 2 nm or less, or about 10 nm to about 50 nm. The height can resultfrom an individual SWNT or for a plurality of SWNTs. Heights can be usedwhich provide for thin film applications or single SWNT transistors.

A plurality of carbon nanotubes can be adsorbed which have an averagelength of at least one micron.

The carbon nanotubes can form an arc or a circle.

Adapting so Carbon Nanotube at the Interface

At least one carbon nanotube is at least partially selectively adsorbedat the interface. The experimental parameters can be adapted asdescribed, for example, in the working examples and discussed in themodeling, so that the carbon nanotube is at least partially selectivelyadsorbed at the interface. Only a portion of the longer nanotube need beat the interface, but in any event, the amount of the nanotube at theinterface is higher than if random distribution of the nanotube waspresent on the first region. For example, at least 10%, or at least 20%,or at least 30% of the length of the carbon nanotube can be disposed atthe interface. In general, this occurs with use of carbon nanotubeswhich are longer than the feature sizes to which they absorb.

In one embodiment, the carbon nanotube is substantially disposed at theinterface of the first and second regions. For example, at least 70%, orat least 80%, or at least 90% of the length of the carbon nanotubes canbe disposed at the interface. Or, for example, for a plurality ofnanotubes, at least 70%, or at least 80%, or at least 90% of the lengthof the nanotubes can be disposed at the interface with the remainingportions leaving the interface to be disposed on in many cases the firstregion rather than the second region.

The carbon nanotube can be horizontally aligned so that it lays on thesubstrate either totally or substantially.

Hence, an embodiment is an article comprising: a solid surfacecomprising at least two different surface regions including: a firstsurface region which comprises an outer boundary and which is adaptedfor carbon nanotube adsorption, and a second surface region which isadapted for preventing carbon nanotube adsorption, the second regionforming an interface with the outer boundary of the first region, atleast one carbon nanotube which is sufficiently long with respect to thesize and shape of the first surface region so that it is at leastpartially selectively adsorbed at the interface.

One skilled in the art can experiment with CNT length and the firstsurface region shape and size to find when the selective adsorption atthe interface becomes important. One can look for an enrichment effectwhere the CNT is not just randomly disposed in the first region.

In one embodiment, the outer boundary is circular. In anotherembodiment, the carbon nanotube forms a ring. In one embodiment, theouter boundary is circular and the carbon nanotube forms a ring. In oneembodiment, the first region comprises a ring or a circular dot. In oneembodiment, the first region comprises a circle with a diameter, and thelength of the carbon nanotube is longer than the diameter.

Nanowires, Nanotube Embodiments

Other examples include nanowires and nanotubes, including inorganicsystems not limited to carbon systems. Different types of nanowiresexist and can be used, including for example metallic (e.g., Ni, Pt,Au), semiconducting (e.g., InP, Si, GaN, ZnSe, CdS, etc.), andinsulating (e.g., SiO₂, TiO₂). Nanowires can be silicon nanowires,metallic nanowires including gold or nickel, and metal oxide nanowires.Other materials useful for forming nanowires include semiconductormaterials including Group II-VI semiconductor materials. Molecularnanowires are composed of repeating molecular units either organic (e.g.DNA) or inorganic (e.g. Mo₆S_(9-x)I_(x)). High aspect ratio nanotubesand nanowires can be used including those having aspect ration of 500 ormore, 1,000 or more, or 5,000 and more. These high aspect ratiostructures can be open or closed, or open but filled with differentmaterial, and can be called wires, rods, tubes, fibers, and the like.Nanowires are described in for example Hong, Seunghun, US PatentPublication 2004/0166233, Depositing Nanowires on a Substrate, which ishereby incorporated by reference in its entirety.

Methods of Making

Another embodiment is the method of making the articles describedherein. For example, an initial step can be providing a solid surfacecomprising at least two different surface regions, a first surfaceregion which comprises an outer boundary and which is adapted for carbonnanotube adsorption, and a second surface region which can be adaptedfor preventing carbon nanotube adsorption. The second region can form aninterface with the outer boundary of the first region.

Various lithographies, microlithographies, nanolithographies, andprinting technologies can be used including for example DPN printing,microcontact printing, nanoimprint lithography, scanning probelithography, electron beam lithography, photolithography, and the like.

In particular, direct-write nanolithography can be used to make thesubstrate. Direct-write technologies can be carried out by methodsdescribe in, for example, Direct-Write Technologies for RapidPrototyping Applications: Sensors, Electronics, and Integrated PowerSources, Ed. by A. Pique and D. B. Chrisey, Academic Press, 2002.Chapter 10 by Mirkin, Demers, and Hong, for example, describesnanolithographic printing at the sub-100 nanometer length scale, and ishereby incorporated by reference (pages 303-312). Pages 311-312 provideadditional references on scanning probe lithography and direct-writemethods using patterning compounds delivered to substrates fromnanoscopic tips which can guide one skilled in the art in the practiceof the present invention.

Direct-write nanolithography, in addition, has been described in thefollowing documents which are each hereby incorporated by reference intheir entirety and form part of the present disclosure. (1) Piner et al.Science, 29 Jan. 1999, Vol. 283 pgs. 661-663. (2) U.S. Pat. Nos.6,635,311 and 6,827,979. (3) Demers et al. Angew Chem. Int. Ed. Engl.2001, 40(16), 3069-3071, (4) Demers et al. Angew Chem. Int. Ed. Engl.2001, 40(16), 3071-3073, (5) M. Zhang et al., Nanotechnology, 13 (2002),212-217 (parallel DPN printing with array of microfabricated probes),(6) A. Ivanisevic et al., J. Am. Chem. Soc., 2001, 123, 12424-12425(particle assembly with opposite charged species), (7) U.S. PatentPublication 2003/0022470 published Jan. 30, 2003 to Liu et al.(“Parallel, individually addressable probes for nanolithography”).

DPN® and DIP PEN NANOLITHOGRAPHY® are trademarks of Nanoink, Inc.(Chicago, Ill.) and are used accordingly herein. In the DPN® printingprocess, which can be carried out using an NSCRIPTOR instrument fromNanoInk, an ink is transferred to a substrate from a tip. Thetransferred ink, if desired, can be used as a template for furtherfabrication. The advantages and applications for DPN® printing arenumerous and described in these references. DPN® printing is an enablingnanofabrication/nanolithographic technology which allows one to practicefabrication and lithography at the nanometer level with exceptionalcontrol and versatility. DPN® printing provides for fine control of thepatterning which is not provided by other methods. However, DPN®printing can also be automated which provides rapid production.Moreover, the structures produced by DPN® printing are generally stable,as DPN® printing allows for the ink to be covalently bonded orchemically adsorbed to the substrate rather than merely physicallyadsorbed or mechanically locked in. DPN printing does not require thatthe substrate surface be made porous to accept the ink in a mechanicallock. Rather, the strategically patterned ink materials, chemicallybound at predefined locations by DPN printing, are then used fordirecting desired materials such as, for example, carbon nanotubes atthe predefined locations on the substrate.

U.S. Patent Publication 2002/0063212, published May 30, 2002 to Mirkinet al., discloses many useful embodiments which are hereby incorporatedby reference including, for example, use of tips (paragraphs 0052-0054);substrates (0055); patterning compounds (0056-0078); tip coating methods(0079-82); patterning (0083-88); alignment (0089); nanoplotter format(0090-0092); multiple patterning compounds (0093); other methods(0094-0095); resolution parameters (0096-0100); uses including arraysand detection methods (0101-0106); software (0107-0128); kits (0129);instruments (0130); and imaging methods (0130-0136). Seven workingexamples are provided (0137-0211), which are incorporated by referencein their entirety. An appendix related to computer software is alsoprovided and incorporated by reference (0212-0264).

This type of nanofabrication and nanolithography in particular can bedifficult to achieve with many technologies that are more suitable formicron scale work.

Another step is providing a liquid composition comprising a plurality ofcarbon nanotubes in at least one liquid solvent. Carbon nanotubes can besuspended or dispersed in the liquid. A true solution need not form. Thesolvent can be an organic solvent, an aromatic solvent, a halogenatedsolvent, a polar solvent, a non-polar solvent, an aprotic solvent, andthe like. Carbon nanotubes can also be suspended with the aids ofsurfactants or polymers. (see for example O'Connell et al., “Reversiblewater-solubilization of single-walled carbon nanotubes by polymerwrapping.” Chemical Physics Letters 2001, 342, 265-271; O'Connell etal., Band gap fluorescence from individual single-walled carbonnanotubes, Science (2002), 297(5581), 593-596.) A variety of methods canbe used to prepare this composition including simple mixing andagitation of the solvent and carbon nanotubes. The composition can bepurified if desired.

Another step is placing the liquid composition on the solid surface sothat at least one carbon nanotube adsorbs to the surface. The liquid canbe left until adsorption is complete. It can be agitated. The methods todo this step are not particularly limited.

Another step is removing the at least one liquid solvent by for examplewashing or evaporation.

FIG. 13 illustrates a device for applying the carbon nanotubes withsolvent. This embodiment provides a method of depositing nanotubesolution from a flat, thin nozzle in proximate contact (via the liquid)with the assembling substrate placed horizontally, e.g., less than 30°from the horizon. The nozzle and the substrate can be placed in relativemotion at a constant rate that allows sufficient time for the nanotubesto contact with the affinity template. This embodiment can be useful forassembly over large areas. The nozzle can have a width W which can be aswide as the substrate used for nanotube deposition. Such a nozzle can bemade and used by methods known in the art.

The solvent dispersion containing nanowires and nanotubes, as needed,can be purified before use.

Methods of Using and Application

Applications and methods of use for carbon nanotubes include for exampleconductive and high strength composites, membranes, transistors, fieldeffect transistors, energy storage and energy conversion devices,sensors, field emission displays and radiation sources, hydrogen storagemedia, nanometer-sized semiconductor devices, probes, and interconnects.The background section also describes applications, as well as thereferences cited herein.

Other examples include transparent conductive thin films and catalystsupports. Ropes can be used in devices such as mechanics-based RAMs.

Filtration membranes can be made wherein the carbon nanotubes do notcross over the areas designed to not bind nanotubes (second regionareas) and follow the shape defined by the interface. Hence, forexample, round holes can be formed. The holes can have a diameter ofabout 10 nm to about 1,000 nm, or about 25 nm to about 500 nm.

Modeling

If desired, the interactions between the surface regions, the carbonnanotubes, and the solvent can be modeled. However, the presentlyclaimed invention in its various embodiments is not limited by theory.

A series of non-limiting working examples are described and discussed.

WORKING EXAMPLES

SWNTs were attracted to the hydrophilic portions of a gold substratepatterned by dip pen nanolithography (DPN) printing and morespecifically to the boundary between hydrophilic and hydrophobic SAMfeatures made of 16-mercaptohexadecanoic acid (MHA) and1-octadecanethiol (ODT), respectively. The process used solvent as acarrying media for the carboxylic acid-terminated features and allowedone to control the manipulation and assembly (aligning, positioning,shaping, and linking) of SWNTs on the micron- to sub-100 nm lengthscale, including over large areas by use of microcontact printing (30)and parallel DPN printing (31).

To evaluate the prospect of using SAM boundaries for controlling theassembly of SWNTs, DPN printing was used to generate patterns of MHAcomprising lines, dots, rings, and even alphabetical letters on a goldsubstrate. The exposed gold regions of the substrate were passivatedwith ODT. A drop of 1,2-dichlorohenzene containing SWNTs was then rolledover the patterned substrates (FIG. 1 a). Because 1,2-dichlorobenzenewets the MHA features but not the ODT passivated regions, SWNTs areguided and localized on the hydrophilic regions of the substrate. As thesolution containing the SWNTs evaporates, the nanotubes are attractedboth to each other and the boundary between the ODT and MH. Thisevaporation creates a high local concentration of the SWNTs at the SAMboundaries and almost exclusive assembly on the MHA features (FIG. 1 b).There is believed to be a strong van der Waals attraction between theSWNTs and the carboxylic acid moieties of the MHA, which is apparent inmolecular modeling studies (see below). Because the tubes are too longto assemble within an individual feature they are organized at theinterface of the SAMs and bent along the perimeter of the features tomaximize the overlap with the MHA feature and minimize the tensionarising from nanotube bending. In the case of dots or rings, thisassembly process results in circular structures and substantial bendingof the SWNTs, the extent of which depends on the radius of curvature(FIGS. 2 and 3). Note that within these features the SWNTs follow theperimeter of the dot and form continuous architectures through intertubelinking.

Circular structures made of SWNTs are unusual (17, 18, 32). Thesestructures show interesting curvature-dependent magnetic and electronicproperties (33, 34). Rings of SWNTs, ≈500 nm in diameter, were firstobserved as a low-yield side product in nanotube synthesis (32).Recently, ring structures were produced in solution by anultrasonication method (17) and ring closure reactions (18). With thepresent approach, such SWNT rings can easily be formed and positioned inan ordered array on a surface (FIG. 2 a). For example, 1- to 3-μm-longnanotubes form ring structures on 170-nm-wide, 650-nm-diameter MHA ringfeatures on an Au surface, with exposed Au passivated with ODT. Theaverage height of each SWNT ring is 6±2 nm, demonstrating that these arestacked intertwined structures. They are about five times thinner thanthe analogous structures formed by ultrasonication (17). By usingshorter SWNTs (about 0.4-1.5 μm), it has been have further demonstratedthat SWNTs readily bend to form sub-μm-sized arcs. Even greater controlis demonstrated by shaping SWNTs into nano letters with this approach(see FIGS. 6 and 7).

To more fully understand and use this system, one can elucidate thedriving force for the assembly process and the resolution at which SWNTscan be patterned. To address the resolution issue, the inventors usedDPN printing to pattern Au substrates with MHA dots and lines withdifferent dimensions over the micrometer to sub-100-nm length scale.This technique allows one to study the process in combinatorial formatunder one set of experimental conditions. These experiments clearly showthat SWNTs assemble on all features studied, including the smallest dots(90 nm in diameter) and the thinnest lines (450×100 nm) (see FIGS. 8 and9).

It was found that the choice of affinity template SAM and passivatingSAM pair is important for achieving this level of precision in themanipulation and assembly of SWNTs. When the passivation layer was1-mercaptoundecanol (MUO) or 11-mercaptoundecyl-penta-ethyleneglycol(PEG-SH), the SWNTs assembled on the MHA features but not along theedges of such structures as in the case of the ODT/MHA system (FIG. 3a-c). Although dots of MUO, PEG-SH, and 11-amino-1-undecane-thiol (AUT),where the gold substrate was passivated with ODT, all show affinitiesfor the SWNTs, the interaction seems weaker as compared with MHA asevidenced by a lower density of SWNTs on such features (FIG. 3 d-f).Surprisingly, although NH₂-SAMs were the focus of previous studies(24-26), MHA showed a higher tendency than AUT to assemble andsurface-confine SWNTs.

Contact angle measurements showed that 1,2-dichlorobenzene wets all butthe ODT SAMs on gold. The static contact angle for 1,2-dichlorobenzeneon ODT SAMs was determined to be 60±2°, whereas the contact angles forthe other SAMs were all <10°. Because the solvent wets the COOH-SAMs butnot the CH₃-SAMs, no solvent remains on the CH₃-SAM as the substrate ispulled from the SWNT solution. In contrast, all of the other surfacesretain a thin liquid film, which results in nonuniform SWNT assembly.Compared with the SAMs of MUO, PEG-SH, and AUT, dot features of suchmaterials with surrounding regions passivated with ODT show higherdensities of SWNTs on the affinity template portions of the surface (seeFIG. 10). These observations strongly suggest that the solvent/substrateinteractions are in part responsible for localizing the SWNTs on the MHApatterns.

When a SWNT is driven close to the MHA pattern in the ODT/MHA system,Monte Carlo simulations show that van der Waals attractions between theMHA and SWNT provide the driving force for assembly. Using a parallelMonte Carlo program package and the Amber force field (35), it wasobtained the following relative interaction energies between a [9,6]SWNT and its surroundings: −0.88 eV per nm SWNT for E_(SwNT/solvent)(the interaction of a SWNT with the 1,2-dichlorobenzene solvent), −0.84eV per nm SWNT for E_(SwNT/solvent) (the interaction with a CH₃-SAM),and −1.05 eV per nm SWNT for E_(SwNT/COOH-SAM) (the interaction with aCOOH-SAM). This ordering, COOH-SAM>>solvent>CH₃-SAM, favors SWNTadsorption from solvent onto the COOH-SAM and not the CH₃-SAM.Interestingly, the interaction of a SWNT with AUT, —087 eV per nm SWNT,is much weaker than that for MHA, manifesting the important role of vander Waals interactions in the assembly of SWNTs. In addition, if thetube is sufficiently long (length greater than the size of the MHAfeature) and flexible, it will maximize its interaction with theCOOH-SAM and minimize strain energy by aligning with the outer boundaryof the COOH-SAM.

By balancing these interaction energies, it can be possible to predictthe size of a COOH-SAM for trapping a SWNT of a given length. For a SWNTwith a fraction X of its length in van der Waals contact with theCOOH-SAMs and the remainder, 1−X, in contact with the CH₃-SAMs, thethermodynamic requirement for assembly is,X−E _(SwNT/COOH-SAM+(1−x)) E _(SwNT/CH3-SAM≦) E _(SwNT/solvent)  [1]

Solving Eq. 1 gives x≧19%. This x value indicates that a [9,6] SWNT canbe stabilized on the surface even if only 19% of its length is incontact with the COOH-SAMs. In other words, a 19-nm-wide stripe of theCOOH-SAM is sufficient for trapping a [9,6] SWNT that is 100 nm inlength, even in the extreme situation where the nanotube isperpendicular to the stripe. For a SWNT making a smaller angle withrespect to the stripe, trapping requires an even smaller stripe width.

Based on the aforementioned observations, this approach appears idealfor the assembly of SWNTs in a dense array on surfaces. Indeed, FIG. 4 ashows an array of parallel aligned SWNTs assembled on MFIA patterns (1μm×130-nm lines at a line density of 5.0×10⁷/cm²) with nearly 100%occupancy. Atomic force microscopy (AFM) heights are consistent withindividual SWNTs or small bundles on each feature. It was found that theline width of MHA required for the assembly is only ≈ 1/10 that of theNH₂-SAMs, resulting in a density>10 times higher than what could beachieved previously (25). The decrease in required line width isessential for the precise assembly of short SWNTs (10-50 nm) forhigh-performance field effect transistors (36).

As the size of the MHA pattern is increased, the same spot is oftenoccupied by additional SWNTs, with the number being approximatelyproportional to the volume of the trapped solution. Because of thestrong van der Waals attraction between SWNTs (−1.22 eV per nm contact),additional SWNTs can be deposited on the same site, intertwining witheach other, and extending to bridge SWNTs on nearby MHA features. As aresult, the spacing between SWNTs cannot be reduced to a distance muchsmaller than the tube length without effecting feature cross-linking orsacrificing SWNT feature occupancy. To reduce the van der Waalsattraction, it was decided to functionalize the SWNT sidewalls withdodecyl groups as described (37). The functionalization increased thesolubility of SWNTs in 1,2-dichlorobenzene and resulted in more uniformassembly. Because the dodecyl groups can be thermally cleaved from thetubes at 200° C. (37), these groups can act as nondestructive spacersfor fine-tuning the interactions between the tubes. Alternatively, onecan take advantage of van der Waals attraction to link tubes to makemore sophisticated interlinked structures. For example, μm-long SWNTswere assembled into arrays of continuous, parallel aligned,sub-μm-spaced nanowires (FIG. 4 b and see FIG. 11). Because of theunusual electrical properties of SWNTs, including an electricalconductivity rivaling copper and a current carrying capacity up to 10⁹A/cm² for metallic SWNTs (38), this technique may enable SWNTs to beused as conductive interconnects in electronics. In another example,individual and bundled SWNTs were linked to follow an MHA path definedby DPN printing, exhibiting extensive flexibility that is favorable formaking electronic interconnects (FIG. 4 c and also see FIG. 12).

The ability to control the shape of SWNTs allows one to engineer theirband gaps by building in strain (39) but, most importantly, thisassembly method provides those skilled in the art with a tool toorganize SWNTs into desirable architectures for a variety of potentialapplications. For example, this approach provides a simple route towardcreating thin structured SWNT films that are currently unattainable.FIG. 5 a demonstrates a SWNT filtration membrane with a thickness ofonly 9±2 nm. The SWNT composition has been characterized and mapped witha Raman confocal microscope (FIG. 5 b). These membranes can be madeuniformly over 1×2 cm by μCP (FIGS. 5 c and d), and their sizes appearto be limited only by the area and patterned structures defined byavailable lithography techniques. The thickness of these membranes canbe controlled down to about 5 nm to about 10 nm, thereby promising anultra-high flux in filtration (40) and structured, transparentconductors potentially useful in flexible displays (8, 41).

In conclusion, the working examples have demonstrated the ability toposition, shape, and link μm-long SWNTs by using the boundaries betweenCOOH- and CH₃-SAMs as affinity templates. Experiments and molecularsimulations show excellent control down to sub-100-nm dimensions.Further control can be carried out by fine-tuning the intertubeinteractions (42) and coupling to other alignment techniques such asLangmuir-Blodgett methods (13) or microfluidics (43). Because there isno specific chemical bonding required, this technique can be effectivefor the directed assembly of other nanoscale building blocks such asnanowires and nanoparticles.

Materials and Methods

Materials. MHA (90%), ODT (98%), MUO (97%), 1,2-dichlorobenzene (99%),and ethanol (200 proof, HPLC grade) were purchased from Sigma-Aldrich.AUT (99%) was purchased from Dojindo Laboratories, Kumamoto, Japan. Ti(99.7%) and Au (99.99%) wires were purchased from Alfa Aesar, Ward Hill,Mass. PEG-SM was prepared as described (44).

SWNT Functionalization and Solution Preparation. Purified HiPcomaterials (45), with an iron impurity<1.4 wt %, were dispersed in1,2-dichlorobenzene by mild sonication using a bath sonicator (Bransonmodel 2510) for 3 min. The resulting dispersion was then centrifuged at50,000×g for 10 min, and the supernatant was sonicated for 3 min. Thisprocess was repeated twice, resulting in a solution containing a highpercentage of individual/small bundles of SWNTs. To minimize SWNTaggregation in solution, low concentrations (5-20 mg/liter) were used.Further improvement in solution uniformity was achieved by sidewallfunctionalization of SWNTs with dodecyl groups (37).

DPN Printing. DPN printing (28, 29) experiments were performed with anatomic force microscope (CP-III, Veeco/Thermomicroscopes, Sunnyvale,Calif.) equipped with a 100-μm scanner and closed-loop scan control andcommercial lithography software (DPNWRITE, DPN System-1, NanoInk,Chicago). Gold-coated commercial AFM cantilevers (sharpened, Si₃N₄, typeA, NanoInk) with a spring constant of 0.05 N/m were used for patterningand subsequent imaging. All DPN patterning experiments were carried outunder ambient conditions (≈30% relative humidity, 20-24° C.). Tips weresoaked in an ink solution (e.g., saturated solution of MHA inacetonitrile) for 20 s, and then blown dry with N₂. MHA features weregenerated on a gold thin film by traversing the tip over the surface inthe form of the desired pattern. Polycrystalline Au films were preparedby thermal evaporation of 10 nm of Ti on SiO_(x) followed by 30 nm of Auat a rate of 1 Å/s and a base pressure≦1×10⁻⁶ Torr.

μCP. Stamps were fabricated in a similar process as described (30). Thestamp was “inked” with 5 mM total alkanethiol solution by gentlyspreading a drop on the surface of the stamp with a Q-tip. After thestamp was dry, patterned structures were generated on the surface bybringing the stamp (by hand) into contact with a clean Au thin film for10 s. Then, the substrate was rinsed with ethanol and dried with N₂. Theregions surrounding the molecular features patterned by DPN or μCP werepassivated with a monolayer of alkanethiol molecules (e.g., ODT) byimmersing the substrate in a 1-mM ethanol solution for 10 min followedby copious rinsing with ethanol and water (Barnstead Nanopure WaterPurification System), alternatively. Finally, the substrate was driedwith N₂.

Monolayer Formation. SAMs of alkanethiol molecules were prepared on Authin films by immersing the substrate in a 1-mM ethanol solution of thecorresponding molecules for 1 h, followed by rinsing with ethanol anddrying with N₂. Static contact angles were measured by using thehalf-angle technique (Tantec, Schaumberg, Ill.).

SWNT Deposition. To a DPN-patterned, μCP-patterned, or monolayer-basedsubstrate was added a drop of 1,2-dichlorobenzene containing 5-20mg/liter of SWNTs. The substrate was then tilted back and forth 5-10° toallow the drop to slowly roll through the patterned area five times.Subsequently, the substrate was rinsed gently with cleani,2-dichlorohenzene to minimize nonspecific binding, and then let to dryin air.

AFM and Raman Characterization. Tapping mode AFM images were taken witha NanoMan AFM system (Dimension 3100, Veeco Instruments, Woodbury,N.Y.). Raman images were obtained with a confocal Raman microscope(WiTec Instruments, Ulm, Germany) with a 633-nm excitation line.

Monte Carlo Simulations. In the Monte Carlo calculations, it wasconsidered only the first three carbon groups in the molecular SAMs;that is, CH₃CH₂COOH and CH₃CH₂CH₃ were used to represent MHA and ODT,respectively. This simplification is reasonable because the rest of thealkyl chain is buried, making negligible contributions to the van derWaals interactions between the —CH₃ group and the SWNT. Each SAM wasconstructed from an ensemble of 961 molecules in a hexagonal array,resulting in an overall simulation area of 13×11 nm. The optimizedgeometries of these molecular SAMs give an averaged intermoleculardistance of 5.0 and 4.5 Å for the COOH- and CH₃-SAMs, respectively.These values are in good agreement with experimental values (46, 47).The optimized geometries of these molecular SAMs and a 10-nm-long [9,6]SWNT, made of 1,221 carbon atoms, were used to calculate theirinteraction energies. To model the interaction between the nanotube andthe solvent in a way that is consistent with the SAM/SWNT interaction, a13-nm droplet, consisting of 9,948 1,2-dichlorobenzene molecules, isfirst optimized and sliced in half. This process creates a flat surfacecomparable in size to the surface of the SAM. The SWNT is then put onthis surface and the energy is minimized with the constraint that theSAMs, the solvent surface, and the nanotube are treated as rigid, i.e.,the nanotube is only allowed to translate and rotate. The resultinginteraction energy between nanotube and solvent can thereby be comparedwith those obtained with that between the nanotube and the SAM. Ofcourse, the total interaction between the nanotube and its surroundingsshould also include the interaction between the solvent and the exposedpart of the SWNT. This nanotube/exposed solvent interaction energy wouldbe the same for all three surfaces and would require significantlyhigher computational effort to include, so it has been omitted from theMonte Carlo simulations.

LISTING OF REFERENCES

All references cited herein are hereby incorporated by reference intheir entirety.

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1. A method comprising: providing a solid surface comprising at leasttwo different surface regions including: a first surface region whichcomprises an outer boundary and which is adapted for carbon nanotubeadsorption, and a second surface region which is adapted for preventingcarbon nanotube adsorption and which forms an interface between theouter boundary of the first region and the boundary of the secondregion, providing a liquid composition comprising a plurality of carbonnanotubes in at least one liquid solvent, placing the liquid compositionon the solid surface, so that at least one carbon nanotube adsorbs tothe surface, removing the at least one liquid solvent, wherein the atleast one carbon nanotube is sufficiently longer than the size and shapeof the first surface region so that at least 10% of the length of the atleast one carbon nanotube is selectively adsorbed at the interface andthe at least one carbon nanotube bends along the perimeter of the firstsurface region.
 2. The method according to claim 1, wherein the carbonnanotube is a multi-walled, a double-walled, or a single wall carbonnanotube.
 3. The method according to claim 1, wherein the carbonnanotubes are assembled as continuous ropes from individual nanotubes.4. The method according to claim 1, wherein the first region compriseshydrophilic groups, and the second region comprises hydrophobic groups.5. The method according to claim 1, wherein the placing step is carriedout with use of a flat, thin nozzle.
 6. The method according to claim 1,wherein the first or second region is formed by depositing a patterningcompound on a substrate from a tip.
 7. The method according to claim 6,wherein the tip is a nanoscopic tip.
 8. The method according to claim 6,wherein the tip is an atomic force microscope tip.
 9. The methodaccording to claim 6, wherein the tip is a hollow tip.
 10. The methodaccording to claim 1, wherein the solvent wets the first surface region.11. The method according to claim 1, wherein the solvent does not wetthe second surface region.
 12. The method according to claim 1, whereinat least 20% of the length of the carbon nanotube is disposed at theinterface.
 13. The method according to claim 1, wherein at least 30% ofthe length of the carbon nanotube is disposed at the interface.
 14. Themethod according to claim 1, wherein at least 70% of the length of thecarbon nanotube is disposed at the interface.
 15. The method accordingto claim 1, wherein at least 80% of the length of the carbon nanotube isdisposed at the interface.
 16. The method according to claim 1, whereinat least 90% of the length of the carbon nanotube is disposed at theinterface.
 17. The method according to claim 1, wherein the firstsurface region comprises a dot, a ring, a line, or a curvilinearstructure.
 18. The method according to claim 1, wherein a plurality ofthe carbon nanotubes are adsorbed which have an average length of atleast 0.4 microns.
 19. The method according to claim 1, wherein thecarbon nanotube has a length of about 10 nm to about 5 microns.
 20. Themethod according to claim 1, wherein the first surface region is a dothaving a diameter of about one micron or less.
 21. The method accordingto claim 1, wherein the first region is a dot having a dot diameter, ora ring having a ring diameter, and the nanotube has a length which islonger than the dot diameter or ring diameter.
 22. The method accordingto claim 1, wherein the first region or the second region have a lateraldimension which is about 100 nm or less.
 23. The method according toclaim 1, wherein the carbon nanotube forms a ring.
 24. A methodcomprising: providing a solid surface comprising at least two differentsurface regions including: a first surface region which comprises anouter boundary and which is adapted for carbon nanowire adsorption, anda second surface region which is adapted for preventing carbon nanowireadsorption and which forms an interface between the outer boundary ofthe first region and the boundary of the second region, providing aliquid composition comprising a plurality of carbon nanowires in atleast one liquid solvent, placing the liquid composition on the solidsurface, so that at least one carbon nanowire adsorbs to the surface,removing the at least one liquid solvent, wherein the at least onecarbon nanowire is sufficiently longer than the size and shape of thefirst surface region so that at least 10% of the length of the at leastone carbon nanowire is selectively adsorbed at the interface and the atleast one nanowire bends along the perimeter of the first surfaceregion.